The self leveling system has two boosters in line to keep the pressure in the system when these two fail your car will sag in the rear after extended standing, and when the system get worse from bad the rear suspension will start bouncing all this will seem cute when it starts, the car rising in the rear when you start it the bouncing over bumps it is not very good for the pump if it keeps up for a long time. I am sure BMW will never admit it but the selfleveling shocks, I think, have always leaked to a small degree.Fareed